1. Field of the Invention
The invention relates to systems for informing users of urban public transport about the real positions at each instant of the transport vehicles that they are considering taking.
2. The Prior Art
The vehicles concerned in this case are more particularly self-propelled surface urban public transport vehicles and they are referred to below by the word "buses".
It is recalled that in general it is not possible to predict exactly the instants at which the buses serving a given line in an urban transport network will serve each of the bus stops or "stops" of the line.
Although the instants at which the various buses leave the departure depot of the line can be determined accurately, it is not possible to know in advance what difficulties each bus will encounter as it travels along the corresponding line, essentially because of the unpredictable formation of more or less dense "holdups" along the line that may slow traffic down or even stop it temporarily.
Thus, in general, users going to one of the various stops of the line for the purpose of taking one of the buses serving it do not know how long they will have to wait for the next bus to arrive.
They are therefore reduced to waiting for the next bus to arrive without knowing whether their wait will be short or otherwise.
This ignorance constitutes a serious drawback for surface urban public transport.
For fear of being obliged to wait a long time for a bus, which time may reach or even exceed quarter of an hour, and may sometimes take place under conditions of relative discomfort, e.g. standing and exposed to bad weather, numerous potential users use some other form of transport, such as an underground railway or a taxi, while regretting that they cannot benefit from the advantages of surface transport such as a pleasant trip associated with a cheap fare.
To remedy this drawback, proposals have already been for certain bus stops to display information relating to the waiting time expected before the next bus arrives.
That constitutes real progress.
However, to obtain such information, a user must actually go to a bus stop that has been improved in that way.
The information then acquired concerning the waiting time for the next bus is certainly advantageous in that it helps the user to be patient if the time is long.
However it loses much of its advantage since the user still has practically no opportunity of avoiding wasting time, since the range of activities that a user can undertake on the spot is generally extremely limited.
To remedy that new drawback, proposals have already been made to made portable appliances available to the users of buses in a network, the appliances including, inter alia, means for displaying the waiting times associated with buses that can be taken (see document EP-A-0 451 756).
That concept is advantageous.
However, in the implementations proposed, each appliance is associated with a single bus stop, such that the problem of informing the user is solved in part only.
Thus, the portable appliance enables the user to be informed remotely about the waiting time for buses at the usual bus stop from which the user makes bus trips, which bus stop is generally close to home, assuming that the appliance is associated with that bus stop.
However, the appliance is incapable of giving any information about the waiting times for buses serving other bus stops in the network.
Unfortunately, it is often for a user's return journey that the information in question would be the most useful, in particular such information would enable a user to spend a few more minutes performing activities away from home, e.g. examining goods on sale in a shop, with such examination possibly also being associated with consulting a specialist.
In addition to the above limitation on performance due to the fact that each appliance is associated with a single bus stop, information systems that have been proposed in the past also suffer from the drawback of being of complex organisation, and therefore slow, thus making it difficult to update the displayed information accurately, with this being for reasons that are explained below.
In said systems, the information transmitted over an electromagnetic path and made use of by bus stops and by portable appliances associated with said stops is the same, and it is generated by a common facility required to serve all of the various stops in the network in question, such that each item of data is associated with an encoded address representative of one of the stops.
The receivers included respectively in a given bus stop and in the appliances associated with said bus stop are therefore of the same type, with the main difference between these two receivers lying in that one of them is fixed while the other one is portable.
The addressed items of information in question relate in particular to the approximate waiting times for the two "approaching" buses expected at the stop in question: the fixed or portable receivers located at said bus stop or in the vicinity thereof then merely decode and display those waiting times.
That kind of organization constitutes considerable overhead since it requires:
a very large number of different signals to be transmitted in succession over the electromagnetic path, which number is theoretically equal to the total number N of stops included throughout the network in question; and
for each signal "addressed" to a given stop, a large number P of constituent information units (generally "binary digits" or "bits"), each signal being required to provide, for example, sufficient data to identify the waiting times for the next two buses expected at the stop in question.
The total number NP of information units to be transmitted over the electromagnetic path in known solutions is therefore very high, and this presents the drawback of requiring a long duration or a high data rate for transmitting all of the information useful to the network.
The long duration means a long period before the transmission is renewed, which transmission is preferably renewed cyclically: a result of the length of this period is a long overall response time, and thus information for display may be updated very late, and this can make the system unusable in practice if the observed delays reach or exceed one minute.
A high data rate means that it is difficult for the transmission considered herein to make use of the sidebands left available by urban radiotelephone transmissions, since said sidebands are too narrow for excessively high rates of transmission.